Hydralazine for Hypertension Treatment

While hydralazine has been largely replaced by other drugs for the treatment of high blood pressure, it still plays an important role in certain conditions, such as for treating severely elevated high blood pressure that does not respond well to other therapies. Hydralazine can be administered in several different ways, making it well suited to situations that require flexibility in dosing.

Person taking high blood pressure medication with box of pills and a glass of water on a white table
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How Hydralazine Works

Hydralazine works by causing the muscles that line and surround the arteries to relax, resulting in vasodilation (widening of the blood vessels) and lowered blood pressure.

While the precise details of how hydralazine causes this relaxation is not known, it is believed that hydralazine interferes with the transfer of calcium inside of muscle cells. Muscles need calcium to contract, so this action results in muscle relaxation.

Along with arterial muscle relaxation, hydralazine also causes an increase in heart rate and an increase in the total amount of blood being pumped by the heart.

Other Drugs like Hydralazine

Hydralazine is formally known as a direct-acting vasodilator, which means that it works directly on the blood vessels themselves to cause relaxation.

While there are many different types of vasodilators used in medicine today, none share the chemical or clinical properties of hydralazine. Though typically dispensed as a generic drug, hydralazine may sometimes still be found as the brand name drug Apresoline.

Side Effects of Hydralazine

Hydralazine tends to increase heart rate and may cause fluid retention through its action on the kidneys. These effects are usually countered when hydralazine is prescribed along with other medicines like beta-blockers and diuretics.

Some common side effects of hydralazine include:

  • Headache
  • Nausea
  • Decreased appetite
  • Diarrhea

Rarely, hydralazine may cause a serious disease known as drug-induced systemic lupus erythematosus, which causes the immune system to attack normal cells. This condition almost always resolves once the hydralazine is stopped.

Notes About Hydralazine

Sometimes, you might be prescribed a medication that isn't commonly used. If that's the case, ask your doctor why the medication was selected for you and how long you should expect to use it. You might have a unique condition, or other more commonly used medications might be contraindicated for you. Be sure to notify your healthcare provider if you are pregnant or breastfeeding, and to supply the names of any other medicines and/or supplements you are taking. Remember to include over-the-counter medicines, like aspirin or Advil (ibuprofen), and herbal/natural supplements.

2 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Bang L, Nielsen-kudsk JE, Gruhn N, et al. Hydralazine-induced vasodilation involves opening of high conductance Ca2+-activated K+ channels. Eur J Pharmacol. 1998;361(1):43-9. doi:10.1016/s0014-2999(98)00701-8

  2. Messerli FH. Vasodilatory edema: a common side effect of antihypertensive therapy. Curr Cardiol Rep. 2002;4(6):479-82. doi:10.1007/s11886-002-0110-9

Additional Reading
  • Sources:
  • Hydralazine Hydrochloride. (n.d.). DRUGDEX® System Retrieved December 4, 2007, from http://www.thomsonhc.com. Greenwood Village, CO: Thomson Healthcare.

By Craig O. Weber, MD
Craig O. Weber, MD, is a board-certified occupational specialist who has practiced for over 36 years.